Orbital tube whip rod heat exchangers, including both evaporators and freezers, have been recently developed and are the subject of several recently issued patents. An example of an orbital tube whip rod heat exchanger used as an evaporator may be found in U.S. Pat. No. 5,221,439 issued Jun. 22, 1993. The orbital tube whip rod construction has been carried forward by the same inventor in constructing a freezer and, for our purposes, more particularly with respect to a drive arrangement for the orbital tube whip rods as shown in U.S. Pat. No. 5,385,645 issued Jan. 31, 1995, and entitled Heat Transfer Apparatus With Positive Drive Orbital Whip Rod, the disclosure of which is incorporated herein by reference. As shown therein, a plurality of tubes are supported by a pair of tube sheets at their upper and lower ends within a vessel. Each tube has a rod extending throughout its length which is driven orbitally about its inner circumference by an upper and lower drive plate. The material to be processed is fed through the interior of the tube and is spread in a thin film over the inner circumference of the tubes by the rods. A refrigerant is circulated within the vessel between the tube plates so as to chill the exterior of the tubes and thereby freeze the processed fluid. An ice crystalline slurry exits the bottom of the tubes and is pumped away to a storage tank or otherwise utilized depending upon the particular application.
Various arrangements are suggested for the mounting and support of the whip rods and various alternatives are suggested for the drive plates. One of the drive plate arrangements addresses the inherent vibration problem which is experienced as induced by the dynamic forces generated by the rods as they are orbitally driven within the freezer. As shown in FIG. 3 of this patent, a pair of orthogonal drive plates supported by eccentric bearings and mounting brackets are oriented 180.degree. apart and each drives half the rods, or whip rods, thereby balancing the mass of the rods. However, this construction requires a pair of vertically spaced, offset drive plates at each of the upper and lower rod ends, the complexity of offset eccentric bearings, and lost space in the area of overlap between the drive plates where tubes may not be placed due to plate-rod interference. This plate-rod interference also dictates a specific and non-uniform placement of the tubes and rods which requires a vessel having a greater cross-sectional area to contain the same number of tubes and rods. Thus, more refrigerant is required to fill the necessarily larger vessel over a vessel containing tubes which are uniformly spaced. For these and other reasons, it is not anticipated that this arrangement will be commercialized.
Still another drawback to the revolutionary designs disclosed in the prior patents is the undesirable obstruction of the drive plate and other supporting structure at the lower ends of the rods and tubes. During the operation of the orbital rod freezer, as mentioned above, a slurry of ice is produced as the process fluid traverses the tubes from top to bottom. It has been found that obstructions at the lower ends of the tubes and rods provide convenient locations for the formation and accumulation of solid ice pack which interferes with and clogs the continuing flow of ice slurry. Although the patent suggests different arrangements for supporting the whip rods and mounting the drive plates, it is not believed to have been contemplated that an orbital rod freezer could be constructed which would be totally unobstructed at the lower tube and rod ends.
In order to solve these and other problems in the prior art, the inventor herein has previously succeeded in designing and developing an improvement to the very valuable and important inventions disclosed relating to the orbital tube whip rod heat exchanger and especially including the orbital rod freezer. The inventor's improvement is disclosed and claimed in the parent cross-referenced above and includes the development of a technique and structure for supporting and driving the whip rods solely at their upper ends while at the same time providing for a dynamic balancing of the forces generated by the rods as they are driven orbitally within the tubes. The inventor achieves these desirable features by utilizing a countercrank associated with each whip rod and tube, the countercrank having at least two whip rod holes, either one of which may receive a whip rod. The whip rod holes are located 180.degree. from each other around the circumference of the countercrank. The rods may thus be installed in an offset manner from one tube to another and driven with a single drive plate in an elegantly simple, efficient arrangement. As the countercranks provide the only driving connection between the drive plate and rods, a single drive plate may be used to drive each countercrank drive pin to achieve a dynamic balancing of the dynamic forces which eliminates vibration in the heat exchanger. Although a countercrank having two or three holes is shown in the preferred embodiments of the invention, it should be understood that other variations may be implemented without departing from the general concept of equally distributing the mass of the rods about the center of the tube pattern, such that the center of mass of each opposed group of rods has a common rotational center, thereby balancing the forces induced, while preventing any unbalanced moments. One such variation would include providing a single whip rod hole, but locating the whip rod hole at different locations in different countercranks which would then become a matched set for the particular number of tubes used in a particular heat exchanger. Other variations also are feasible including varying the mass of the rod itself.
The rod is supported within the whip rod hole by a top hat or flange at its upper end which is larger in diameter than the whip rod hole. The whip rod is thus suspended within the tube by the countercrank. This permits the bottom of the tube and rod to be free from obstruction in that there are no drive plates or rod supports. As explained above, this arrangement is ideal at least in the orbital rod freezer as it eliminates any structure which could accumulate and help form ice pack from the ice slurry which streams out the bottom of the tubes.
Still another advantage of the use of the countercrank is that various arrangements can be made for actually supporting the drive plate itself on top of the countercrank and the countercrank may then in turn be supported from the tube sheet, tube, or combination thereof, or even a replaceable bearing plate to further simplify and streamline the construction of the orbital rod freezer. This simplification and streamlining is important in that the drive plate may be driven at an orbital speed which could induce significant wear to other more complex or inelegant arrangements. Also, more complicated mechanical arrangements with bearings or the like add expense and potential for mechanical failure.
While the inventor's previous development of the countercrank solves many problems with the prior art, and provides many functional advantages which were not previously available, one problem which remained was the inability to provide for the potential for clogging of individual tubes in a multi-tube heat exchanger. For example, when the heat exchanger is used to create an ice slurry, it is possible that individual tubes may begin to accumulate ice along the inside wall of the tube. When this happens, binding between the whip rod and the countercrank occurs which can result in either the countercrank breaking (when constructed of plastic) or dislodging of the countercrank drive pin from its associated drive plate. With the present system controls, blockage of one or several tubes will not typically provide enough of a loss in performance to trigger system monitoring equipment so as to shut down the entire heat exchanger. For example, monitoring of operating temperatures and refrigerant line pressures would not sense the small loss in performance if only several tubes out of a multiple-tube bundle should freeze. Therefore, not only might some time pass before the failure would be detected, but the system would continue to run and potentially cause greater damage.
In order to eliminate any potential equipment damage or maladjustment, while also accommodating the possibility of individual tubes becoming frozen or clogged, the inventor herein has succeeded in designing and developing an improvement to his countercrank which includes a radially-oriented slot extending from the center of the countercrank to the periphery thereof for receiving a whip rod. As the countercrank rotates, centrifugal forces will move the whip rod toward, but not in contact with the outermost or peripheral end of the slot which is the normal operating position for the whip rod to circulate around the inner sidewall of the tube. In the event that a layer of ice or other obstruction forms along the inner surface of the tube wall, the whip rod may automatically self-adjust by migrating radially inward. In this manner, the whip rod may continue its job, to the extent possible, by wiping along the inner surface of what may be an ice buildup to provide for continued heat transfer although at lesser efficiency. Should the condition continue, the whip rod is capable of migrating to the center of the countercrank where it may even be frozen solid in place. If this extreme event occurs, the countercrank may continue to rotate within the tube and about the now centrally-located whip rod without any increased force required or undesirable forces being exerted against any of the equipment including the countercrank, drive pin/drive plate arrangement, or tube. In this manner, and with this improved design, individual tubes in a multiple-tube heat exchanger bundle may be permitted to freeze solidly and yet other tubes may continue to function without damage to the drive plate, countercrank, tube combination.
While the principal advantages and features of certain specifics of the preferred embodiments have been explained above, a greater understanding of the invention may be attained by referring to the drawings and detailed description of the preferred embodiment which follow.